Run code only when monitoring is enabled

Setting up the monitor sockets is only usefull when actully using
heartbeat monitoring, so only run it in that case.

IPython/parallel/engine/engine.py

@@ -178,6 +178,8 b' class EngineFactory(RegistrationFactory):'
             hb_ping = maybe_tunnel(url('hb_ping'))
             hb_pong = maybe_tunnel(url('hb_pong'))
             
+            hb_monitor = None
+            if self.max_heartbeat_misses > 0:
             # Add a monitor socket which will record the last time a ping was seen
             mon = self.context.socket(zmq.SUB)
             mport = mon.bind_to_random_port('tcp://127.0.0.1')
@@ -185,8 +187,7 b' class EngineFactory(RegistrationFactory):'
             self._hb_listener = zmqstream.ZMQStream(mon, self.loop)
             self._hb_listener.on_recv(self._report_ping)
             
-            hb_monitor = None
-            if self.max_heartbeat_misses > 0:
+            
                 hb_monitor = "tcp://127.0.0.1:%i"%mport
 
             heart = Heart(hb_ping, hb_pong, hb_monitor , heart_id=identity)